3-axis accelerometer with gap-closing capacitive electrodes

Abstract

Disclosed is a novel three-axis capacitive-type accelerometer implemented on SOI wafer. The accelerometer consists of four springs, one proof mass, four pairs of gap-closing sensing electrodes (each pair of gap-closing sensing electrode containing one movable electrode and one stationary electrode), and several metal-vias as the electrical interconnections. The movable electrodes are on the proof mass, whereas the stationary electrodes are fixed to the substrate. The three-axis accelerometer has five merits. (1) The sensitivity of the accelerometer is improved since the proof-mass is increased by containing both device and handling silicon layers; (2) The sensitivity is also improved by the gap-closing differential capacitive sensing electrodes design; (3) The parasitic capacitance at bond pad is reduced by the existing of metal-vias between the device Si layer and handling Si layer; (4) The sensing gap thickness is precisely defined by the buried oxide of SOI wafer; (5) The stationary sensing electrodes anchored to the substrate also act as the limit stops to protect the accelerometer.

What is claimed is: 
     
       1. A sensing accelerometer, comprising:
 a substrate further comprising:
 at least four fixed electrode plates; and 
 
 a movable unit further comprising:
 a movable electrode having at least four edges; and 
 plural components connected to the substrate and the movable element, 
 
 wherein the plural components are flexible components, the substrate is a fixing substrate and comprises plural fixed anchors respectively connected to the plural flexible components, the at least four fixed electrode plates are disposed beside the at least four edges of the movable electrode so as to sense an X-axis, a Y-axis and a Z-axis accelerations, each of the at least four plural fixed electrode plates and the movable electrode has a via disposed therein, and the at least four plural fixed electrode plates comprises:
 plural lower electrode plates respectively placed along a first group of the plural edges of the movable electrode, and providing a lower limit of the movable unit in the Z-axis movement, wherein the first group of the plural edges has an even total number, and includes plural pairs of associated opposite edges; and 
 plural upper electrode plates respectively placed along a second group of the plural edges of the movable electrode, and providing an upper limit in the Z-axis movement for the movable unit, wherein the second group of the plural edges has an even total number, and includes plural pairs of associated opposite edges, 
 wherein each of the plural lower electrode plates has a portion being held under the movable electrode, and each of the plural upper electrode plates has a portion being held over the movable electrode. 
 
 
     
     
       2. The accelerometer according to  claim 1 , wherein the substrate has plural inner edges each of which has an opposite one of the plural inner edges. 
     
     
       3. The accelerometer according to  claim 1 , wherein each of the plural fixed anchors has a corner, and the plural flexible components connect the respective corners of the plural fixed anchors. 
     
     
       4. The accelerometer according to  claim 1 , wherein each of the plural fixed anchors has an via disposed therein. 
     
     
       5. The accelerometer according to  claim 4 , wherein the substrate and the movable unit are made of a Silicon on Insulator (SOI) wafer, and the respective vias conduct the substrate and the movable unit. 
     
     
       6. The accelerometer according to  claim 4 , wherein the respective vias are formed by one selected from a group consisting of a silver paste, a polycrystalline silicon deposition and a metal sputtering. 
     
     
       7. The accelerometer according to  claim 1 , wherein the movable unit and each of the fixed electrode plates have a gap therebewteen, and the movable electrode and the at least four fixed electrode plates form at least four pairs of differential type capacitive sensing electrodes. 
     
     
       8. The accelerometer according to  claim 1 , wherein each of the plural components is a spring. 
     
     
       9. The accelerometer according to  claim 1  being a capacitive sensing accelerometer with at least four pairs of gap-closing differential electrodes formed by the movable electrode and the at least four fixed electrode plates. 
     
     
       10. A multi-axes accelerometer, comprising:
 plural fixing elements; 
 a movable electrode having plural edges with a first and a second groups, and having plural components respectively connected to the plural fixing elements; and 
 plural stationary electrode plates configured beside the movable electrode, and classified as:
 plural lower electrode plates respectively placed along the first group of the plural edges of the movable electrode, and providing a lower restriction of the movable unit in a Z-axis movement; and 
 plural upper electrode plates respectively placed along the second group of the plural edges of the movable electrode, and providing an upper limit of the restriction movable unit in the Z-axis movement, 
 
 wherein each of the plural lower electrode plates has a portion being held under the movable electrode, each of the plural upper electrode plates has a portion being held over the movable electrode, each of the plural stationary electrode plates and the movable electrode has a via disposed therein, and the multi-axes accelerometer is a capacitive sensing accelerometer with at least four pairs of gap-closing differential electrodes formed by the movable electrode and the plural stationary electrode plates so as to sense an X-axis, a Y-axis and a Z-axis accelerations, and 
 wherein the plural fixing elements are plural fixing anchors. 
 
     
     
       11. The accelerometer according to  claim 10 , wherein each of the plural fixing anchors, each of the plural stationary electrode plates and the movable electrode are made of a Silicon On Insulator (SOI) wafer, each of the plural fixing anchors has a via configured therein, and the respective vias conduct the plural fixing anchors, the plural stationary electrode plates and the movable electrode. 
     
     
       12. A multi-axes accelerometer, comprising:
 a movable electrode having plural edges with a first and a second groups; and 
 plural stationary electrode plates classified into plural lower stationary electrode plates and plural upper stationary electrode plates, 
 wherein the plural lower stationary electrode plates are respectively configured along the first group of the plural edges and provide a lower limit of the moving limit, the plural upper stationary electrode plates are respectively configured along the second group of the plural edges and provide an upper limit of the moving limit, the movable electrode and each of the plural stationary electrode plates have a gap therebetween, the plural stationary electrode plates are respectively configured to form at least four pairs of electrodes with the movable electrode so as to sense at least an X-axis, a Y-axis and a Z-axis accelerations, and each of the plural stationary electrode plates and the movable electrode has a via disposed therein. 
 
     
     
       13. The accelerometer according to  claim 12  further comprising a fixing substrate having plural anchors and the plural stationary electrode plates, wherein the movable electrode has plural flexible components respectively connected to the plural anchors. 
     
     
       14. The accelerometer according to  claim 12 , wherein the plural stationary electrode plates are differential type capacitive sensing electrodes.